The present invention relates to novel acid- and amine-functional polymers, and a method for their preparation. This method is useful in aqueous systems, polar solvent systems, nonpolar solvent systems, or any combination thereof. The method of the present invention is especially useful in preparing latex compositions, as it involves incorporating an amine functionality into an anionically stabilized latex.
The phrase "anionically stabilized latex" refers to a latex that derives colloidal stability from the presence of either adsorbed or chemically bound anionic groups at or near the surface of the latex particle. Anionic stabilizers are usually preferred over cationic stabilizers for latex synthesis as they are readily available, are relatively low in cost, and provide a high degree of colloidal stability to the latex at relatively low use levels. Yet, those skilled in the art of emulsion polymerization are aware that imparting cationic properties to a latex can be very beneficial for improving the performance properties of the resultant coatings.
Incorporation of amine functionality into an anionically stabilized latex is very difficult. One known method is the use of amine-containing monomers with acid-containing monomers during polymerization. The main drawback to this is that, with typical single stage anionic polymerizations, introduction of the strongly basic, polar, amine-containing monomers results in the generation of cationic polymeric species, which flocculate and coagulate the anionically stabilized latex particles to such a degree that resulting latexes have little or no commercial value. In addition, there may be severe reactor clean-up problems due to accumulation of excessive amounts of coagulum within the reactor.
U.S. Pat. No. 3,404,114 (Snyder et al.) and U.S. Pat. No. 4,760,110 (Das) both teach 2-stage methods for preparing acid- and amine-functional latexes without coagulation, wherein an acid functional latex is formed first, then the pH of the emulsion is raised by addition of base, and finally the amine functionality is introduced by addition of an amine-functional monomer. The primary disadvantage to these methods is that they are prepared by the 2-stage polymer process which isolates the acid and amine moieties in separate polymer chains within the latex particle.
Certain types of acid-amine solution polymers are known, wherein amine monomer, e.g., dimethylaminoethylmethacrylate, is polymerized with methacrylic acid or other acrylic esters. The main limitation of these types of acid-amine polymers is that there are relatively few amine-functional monomers available.